The effects of HBr/Ar and HBr/Cl-2 mixing ratios in the ranges of 0-100% Ar or Cl-2 on plasma parameters, densities of active species influencing the dry etch mechanisms were analyzed at fixed total gas flow rate of 40 sccm, total gas pressure of 6 mTorr, input power of 700 W and bias power of 300 W. The investigation combined plasma diagnostics by Langmuir probes and the 0-dimensional plasma modeling. It was found that the dilution of HBr by Ar results in maximum effect on the ion energy flux with expected impact on the etch rate in the ion-flux-limited etch regime, while the addition of Cl-2 influences mainly the relative fluxes of Br and Cl atoms on the etched surface with expected impact on the etch rate in the reaction-rate-limited etch regime.